The present invention relates to computer-aided design (CAD) processes and, more particularly, to a method for creating a three-dimensional CAD solid model of a component from the numerically controlled (NC) fabrication instructions for the component that were previously used to fabricate the component by NC machining procedures.
Many engineering designs of machined components in current use were initially developed. prior to or without the aid of CAD systems and, consequently, electronic representations of such designs do not exist. Accordingly, updating or making modifications to such component designs using current CAD processes requires first creating a computer-based digital representation of the component. Although methods have been developed for creation of computer-based representations from component drawings, photographs, and/or shop measurements, these methods are tedious, expensive, and often produce inaccurate results.
In cases where a component has been fabricated using NC machining processes, the NC instruction file or xe2x80x9cbookxe2x80x9d contains fabrication instructions for NC machines to follow to produce all or part of that component from a piece of raw stock material, such as a metal billet. The stock material is often referred to in the CAD environment as a xe2x80x9ctool solid.xe2x80x9d Broadly, the NC file describes the paths along which the fabrication machine operates one or more rotating cutting tools upon the tool solid to create the machined component.
Other processes have been used to generate engineering data from NC files; however, the output from these processes has been in the form of point clouds and Stereo Lithography (STL) files, which are not fully compatible with modern CAD systems. As known in the art, a point cloud comprises a plurality of coordinates for individual points that represent locations on the surface of an object. A point cloud can be generated through scanning or digitizing. An STL format model represents the surface of an object by a plurality of triangles, each triangle defined by the coordinates of its three vertices and a single normal vector directed away from the object""s surface. Thus, these methods require extensive processing of the output files before the results can be utilized on a CAD system. Accordingly, it would be desirable to have a reliable, inexpensive, and accurate method of creating a CAD solid model of a component from the machine fabrication instruction file used for its fabrication.
A method of satisfying that need and providing still other benefits has now been developed. Broadly, the present invention provides a method for creating a three-dimensional computer-aided design (CAD) solid model of a manufactured component from a numerically controlled (NC) machine fabrication instruction file. The method employs boundary representation (xe2x80x9cB-Repxe2x80x9d) models to define the geometric solids that represent the initial tool solid, the segments of the initial tool solid removed in the specified cutting tool operations, and the finished component. A B-Rep model represents a solid by defining its bounding surface as one or more geometric figures including points, planes, planar polygons, and spline surfaces. Starting with information contained in or derived from the NC file, such as initial tool solid dimensions, cutting tool paths, and cutting tool geometry, by successively redefining the boundaries of the machined tool solid as it is reduced through each specified tooling operation, a CAD solid model of the finished component can be generated. The method generates a three-dimensional representation of an object by creating a model of an initial tool solid with spatial boundaries that define a volume greater than that of the object, creating a model of the segment of the tool solid removed in each tooling operation (a xe2x80x9ctool path solidxe2x80x9d), and then subtracting each tool path solid from the initial tool solid model. The process of creating the model of each tool path solid removed can be simplified by representing the tool paths as geometric forms comprising straight line segments, arcs, spline curves, and planar segments if the deviation of the actual tool path from the perfect geometric models falls within user-defined tolerances.
The preferred process comprises two phases: preprocessing of the NC instruction files and simulation of the machining process. In the initial phase, preprocessing of the NC instruction files, irrelevant data, that is, those data that do not define cutting tool dimensions or tool paths of material cutting (xe2x80x9cmachiningxe2x80x9d) operations, are eliminated. The remaining data, which comprise points defining the tool paths, are analyzed for potential representation as geometric forms comprising straight-line segments, arcs, planar segments, and B-spline curves (a form of Bezier curve defined by a uniform polynomial spline basis function). If the points defining the tool paths fall within user-defined tolerance ranges from theoretically perfect arcs, planar segments, and B-spline curves, the tool paths are approximated the by the corresponding geometric models. These geometric models can be more efficiently manipulated than the multiple individual points defining the tool paths by a computer program implementing the process, thus minimizing simulation processing time. Tool path segments that fall outside the user-defined tolerances for the arcs, planar segments, B-spline curves, etc., are modeled as a series of straight-line segments between successive tool path points.
After the NC instruction files are input, the user may initiate the automatic mode of the preprocessing (first) phase. Upon completion of the automatic preprocessing, the user has the option to further preprocess the data by reviewing all or selected portions of the data for concurrence with the determinations made during automatic preprocessing as to whether that portion of data defines points on a machining tool path, and whether the portion of the data was properly designated for modeling as one of the pre-established geometric forms. If the user determines that modification of any of the preprocessing determinations is necessary, the user may elect to recategorize any portion of the data regarding whether that portion defines points on a machining tool path, and if appropriate, the geometric model designation assigned to a machining tool path.
The second phase of the preferred process, machining simulation, begins with the creation of a solid model representing an arbitrary xe2x80x9cinitial tool solid,xe2x80x9d that is, a representation of one possible configuration of a raw material solid with spatial boundaries sufficient to encompass all of the tool paths specified in the machining instruction files. Then the program simulates the machining operation defined by each tool path in the NC file, creating a tool path solid, which represents the segment of discarded material removed by the cutting tool as it travels along the prescribed tool path. Finally, each tool path solid is mathematically subtracted from the initial tool solid, with the remaining mathematical xe2x80x9csolidxe2x80x9d being the CAD model of the finished component. This modeling and subtraction of each tool path solid in the simulation phase may be selectively viewed and monitored by the operator in a user-interactive mode or accomplished autonomously by the program in a bulk processing mode.
The method of the present invention can also be used to visualize, analyze, and troubleshoot existing NC machine instructions. By selecting the user-interactive mode of the machining simulation process, the operator can visualize the cutting operations along the tool path defined by selected instructions, along with the resulting machined tool solid, to confirm the accuracy, appropriateness, and efficiency of the instructions to produce the desired end product. This verification capability enables errors and/or inefficiencies in fabrication instructions to be detected and corrected prior to actual production, thus enhancing quality and minimizing the cost and time required for production.
Broadly, in one aspect, the present invention concerns a method of generating a computer-based three-dimensional representation of an object that can be fabricated by a cutting tool operating along defined tool paths within an initial tool solid, from data containing the cutting tool dimensions and defining points on the tool paths, by creating mathematical models of the initial tool solid and the tool path solid removed along each tool path and mathematically subtracting each tool path solid model from the initial tool solid model.
In another aspect, the present invention concerns a method of generating a computer-based three-dimensional representation of an object that can be fabricated by a cutting tool operating along defined tool paths within an initial tool solid, from data containing the dimensions of the cutting tool, the dimensions of the initial tool solid, and defining points on the tool paths, by creating mathematical models of the initial tool solid and the tool path solid removed along each tool path and then mathematically subtracting each tool path solid model from the initial tool solid model.